sync: update docs and error messages to reflect fixes to overlap checks

cmd/sync/sync.go

@@ -49,6 +49,11 @@ extended explanation in the [copy](/commands/rclone_copy/) command if unsure.
 If dest:path doesn't exist, it is created and the source:path contents
 go there.
 
+It is not possible to sync overlapping remotes. However, you may exclude
+the destination from the sync with a filter rule or by putting an 
+exclude-if-present file inside the destination directory and sync to a
+destination that is inside the source directory.
+
 **Note**: Use the ` + "`-P`" + `/` + "`--progress`" + ` flag to view real-time transfer statistics
 
 **Note**: Use the ` + "`rclone dedupe`" + ` command to deal with "Duplicate object/directory found in source/destination - ignoring" errors.

docs/content/docs.md

@@ -582,7 +582,8 @@ been added) in DIR, then it will be overwritten.
 
 The remote in use must support server-side move or copy and you must
 use the same remote as the destination of the sync.  The backup
-directory must not overlap the destination directory.
+directory must not overlap the destination directory without it being
+excluded by a filter rule.
 
 For example
 

fs/fs.go

@@ -40,7 +40,7 @@ var (
 	ErrorNotAFile                    = errors.New("is not a regular file")
 	ErrorNotDeleting                 = errors.New("not deleting files as there were IO errors")
 	ErrorNotDeletingDirs             = errors.New("not deleting directories as there were IO errors")
-	ErrorOverlapping                 = errors.New("can't sync or move files on overlapping remotes")
+	ErrorOverlapping                 = errors.New("can't sync or move files on overlapping remotes (try excluding the destination with a filter rule)")
 	ErrorDirectoryNotEmpty           = errors.New("directory not empty")
 	ErrorImmutableModified           = errors.New("immutable file modified")
 	ErrorPermissionDenied            = errors.New("permission denied")